Transforming growth factor-beta signals through its cell surface receptor to regulate genes involved in cell cycle arrest and fibrosis. The direct downstream signalling molecule activated by the type I TGF-beta receptor is:

• A STAT3 dimerization in the cytoplasm
• B Ras activation through recruitment of Grb2-SOS complex
• C Hydrolysis of PIP2 to generate IP3 and diacylglycerol
• D Phosphorylation of SMAD proteins at serine residues ✓

Explanation

TGF-beta uses a unique receptor class with intrinsic serine-threonine kinase activity. The ligand-bound type II receptor phosphorylates and activates the type I receptor, which then phosphorylates receptor-regulated SMADs (SMAD2 and SMAD3) on serine residues. These complex with SMAD4 and move to the nucleus as transcription factors. STAT3 belongs to cytokine-JAK signalling, PLC hydrolysis defines Gq-coupled receptors, and Grb2-SOS-Ras is the route taken by receptor tyrosine kinases such as EGF receptor.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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